Inflammatory bowel diseases (IBDs) in humans are complex chronic inflammatory disorders of largely unknown cause. Several mouse models that in some respects resemble human IBDs have recently been developed and have provided new insights into immunoregulatory processes in the gut. Both genetic and environmental factors have been shown to be involved in chronic intestinal inflammation. In most of the models CD4⁺ T lymphocytes have been identified as central mediators of inflammation. Inappropriate activation of T_H1-dominated cytokine pathways upon contact with luminal bacterial antigens and lack of tolerance appear to be crucial for intestinal pathology. We present a brief overview of important animal models of IBD and describe the recent progress in understanding the mechanisms that contribute to chronic intestinal inflammation. Furthermore, novel immunotherapeutic approaches derived from such animal models are discussed.